1. Technical Field
The present invention relates to a device and a method for processing cement kiln combustion exhaust gas to remove harmful substances such as dust, NOx, persistent organic pollutants including dioxins, a volatile organic compound and CO.
2. Background Art
As shown in FIG. 2, a cement burning facility 21 comprises a preheater 22, a calciner 23, a cement kiln 24, a clinker cooler 25 and so on, and cement raw meal R, which is fed to the preheater 22 from raw material supplying system, is preheated in the preheater 22, calcined in the calciner 23, burned in the cement kiln 24, and produced clinker is cooled in the clinker cooler 25. Here, the combustion exhaust gas from the cement kiln 24 is processed through desulferization in the preheater 22 and dust collection using an electric precipitator 26 since limestone as a main raw material has a property to adsorb SOx, and processed combustion exhaust gas is discharged in the atmosphere through a fan 27 and a stack 28.
Although there was not much harmful substance contained in the combustion exhaust gas from the cement kiln 24, such as alkali, chlorine, sulfur, and heavy metal and so on, since it is expected, with the increase in the amount of recycle raw materials and fuels processed by a cement manufacturing facility in recent years and a future increase plan, that the amount of the harmful substance increases, there is a possibility of becoming a problem from now on.
Then, in order to remove the above-mentioned harmful substances, for example, a technology is described in the first patent document. This technology comprises the steps of: bleeding a part of combustion exhaust gas from the inlet hood of a cement kiln; supplying cooling air to the bled gas to cool it to 600-800° C.; introducing the cooled exhaust gas into a cyclone to catch coarse grain dust through separation; introducing the caught coarse grain dust to the kiln inlet hood for circulation; introducing a part of cyclone exhaust gas to the kiln inlet hood to recover heat of the remainder of cyclone exhaust gas; and feeding the exhaust gas to a dust collector to remove fine grain dust.
Furthermore, for the same object as the above, a technology is described in the second patent document. This technology comprises the steps of: sampling preheated raw meal introduced to a kiln inlet hood to analyze the content of harmful substance therein; controlling the amount of emission that circulates from a cyclone to a kiln inlet hood so that an analysis result becomes desired value; controlling a cooling air flow rate so that cyclone inlet gas temperature becomes in the range of 600-800° C.; and simultaneously detecting the cooling air flow rate and the amount of the emission, and controlling the amount so that the amount of emission discharged out of a system from the dust collector becomes approximately equal to the cooling air flow rate.
Moreover, a technology is described in the third patent document, which comprises the steps of: supplying fuel from a fuel-supply opening, and waste containing ammonium nitrogen from the fuel-supply opening and/or its neighborhood to burn them; and introducing gas containing ammonia into a part of 700° C. or more in the phase before burning the waste containing ammonium nitrogen to reduce the amount of NOx generated and not to sprinkle offensive odor at the suppression of the NOx.
Furthermore, in the forth patent document, in order to effectively collect low-melting compounds from the exhaust gas of cement burning facility, a method and a device are disclosed, in which a part of exhaust gas is bled from cement burning facility to collect low-melting compounds; then the temperature of the bled exhaust gas is brought to 1100-1500° C.; and then the bled exhaust gas is quenched to 120-600° C. to collect the low-melting compounds.    Patent document 1: Japanese Patent Publication No. Heisei 11-130489 gazette    Patent document 2: Japanese Patent Publication No. Heisei 11-130490 gazette    Patent document 3: Japanese Patent Publication No. 2000-130742 gazette    Patent document 4: Japanese Patent Publication No. 2003-277106 gazette